1. Field of the Invention
This invention relates to a fine-grain silver oxide powder particularly suitable as a filler for a conductive paste.
2. Background Art
In the semiconductor field, recent advances in integration density and speed have created a need for finer circuit board wiring and more sophisticated multilayer structures. This has in turn led to a need for silver of a finer particle size for use as a wiring material to be incorporated in conductive paste. In addition, the availability of an ultra-fine-grain silver can be expected to promote application to low-temperature bonding paste and printing of wiring patterns by the inkjet method.
Conventionally, ultra-fine particles of silver have been produced chiefly by vapor deposition. This method of production is unavoidably expensive because it is a slow process requiring a large amount of energy.
Technologies have been developed for using silver oxide as a wiring material, either in place of or together with silver. DENSHI ZAIRYOU(Electronic Materials), July 2003, Vol. 42, P. 97–101, for example, describes use of silver oxide as a filler for conductive paste and proposes inclusion of an appropriate reducing agent in the paste. It is said that when the paste is heated, the silver oxide is reduced to silver and the silver particles simultaneously fuse to form a conductor. On the other hand, JP2001-35255 A teaches a fluid dispersion obtained by individually dispersing silver-containing ultra-fine particles of under 10 nm in an inorganic solvent and says that the silver-containing ultra-fine particles can be silver, silver oxide or a mixture thereof.